Add klass level between student and section

stages/fixtures/test_fixture.json

@@ -20,6 +20,14 @@
       "name": "EDE"
     }
   }, 
+  {
+    "pk": 1, 
+    "model": "stages.klass", 
+    "fields": {
+      "name": "1ASE3",
+      "section": 1
+    }
+  }, 
   {
     "pk": 1, 
     "model": "stages.student", 
@@ -27,7 +35,7 @@
       "city": "La Chaux-de-Fonds", 
       "first_name": "Albin", 
       "last_name": "Dupond", 
-      "section": 1, 
+      "klass": 1, 
       "pcode": "2300", 
       "birth_date": "1994-05-12"
     }
@@ -39,7 +47,7 @@
       "city": "Neuch\u00e2tel", 
       "first_name": "Justine", 
       "last_name": "Varrin", 
-      "section": 1, 
+      "klass": 1, 
       "pcode": "2000", 
       "birth_date": "1994-07-12"
     }
@@ -51,7 +59,7 @@
       "city": "Cernier", 
       "first_name": "Elvire", 
       "last_name": "Hickx", 
-      "section": 1, 
+      "klass": 1, 
       "pcode": "2053", 
       "birth_date": "1994-05-20"
     }
@@ -63,7 +71,7 @@
       "city": "La Sagne", 
       "first_name": "Andr\u00e9", 
       "last_name": "Allemand", 
-      "section": 1, 
+      "klass": 1, 
       "pcode": "2314", 
       "birth_date": "1994-10-11"
     }